Diphtheria is an infection caused by the Corynebacterium and is spread via air and direct contact. The symptoms often present gradually over a couple of days with a sore throat and fever. In severe cases, a grey or white patch develops in the throat, which can block the airway and create a barking cough. Diphtheria can also cause a swollen neck, sometimes referred to as a bull neck. The disease is fatal in between 5% and 10% of cases. In children under five years old and adults over 40 years, the fatality rate may be as much as 20%
Diphtheria was first described in the 5th century BC by Hippocrates, but it was not until 1883, that Edwin Klebs identified the bacterium.
In 1897, Paul Ehrlich developed a standardised unit of measure for diphtheria antitoxin. This was the first ever standardisation of a biological product, and played an important role in future developmental work on sera and vaccines.